1. Field of the Invention
The present invention relates to a gypsum-based building material which has an ability to suppress generation of hydrogen sulfide caused by decomposition of an organic material as disposed. More particularly, it relates to a gypsum-based building material which suppresses, over a long period of time, generation of hydrogen sulfide by the action of sulfate-reducing bacteria, when it is landfilled as waste.
2. Discussion of Background
In recent years, along with shortage of landfill sites of waste and increase of landfill costs, there have been illegal dumping of industrial wastes such as building material wastes in suburbs, or organic sludges, waste materials and combustible wastes which should not be brought in least controlled landfill sites have been disposed in such a state as mixed with items permitted to least controlled landfill sites. At such sites, hazardous hydrogen sulfide is often generated, which creates a social problem. This is caused in such a manner that a sulfide (sulfide ions) formed by reduction of sulfuric acid ions by sulfate-reducing bacteria, tend to be dispersed as hydrogen sulfide in the atmospheric air.
It is generally known that as conditions for generation of hydrogen sulfide at landfill sites, in the presence of {circle around (1)} water, {circle around (2)} an organic substance, {circle around (3)} sulfate ions and {circle around (4)} sulfate-reducing bacteria, it is necessary to maintain {circle around (5)} anaerobic condition, {circle around (6)} pH=4 to 9, and {circle around (7)} a proper temperature, and hydrogen sulfide will be generated only when all of these conditions are met.
Gypsum-based building materials, particularly gypsum boards, are used in a large quantity as interior materials of buildings because of their convenience. While a recycling route is established for discard materials at the time of new construction, recycling of waste materials at the time of demolition has just been started, and most of such waste materials are still dumped together with other building waste materials at landfill sites.
Properly disposed gypsum board waste materials will not create any problem. However, if at a landfill site, in addition to the above gypsum board waste materials, a large amount of organic materials which should not be brought in, are dumped, and the above-mentioned conditions are all met, gypsum as the main component of the gypsum boards, i.e. calcium sulfate, will serve as a supply source of sulfate ions and thus will cause generation of hydrogen sulfide for a long period of time.
Such hydrogen sulfide is formed in a metabolic process wherein sulfate-reducing bacteria active in an anaerobic condition utilizes an organic substance such as lactic acid as an electron donor and finally donates electrons to a sulfate to acquire an energy. Heretofore, 5 various methods have been proposed to suppress generation of hydrogen sulfide caused by such an action of sulfate-reducing bacteria.
For example, utilization of inorganic compounds such as nitrates, nitrites or iron sulfate (JP-A-10-85785, JP-A-11-206863), utilization of various antibacterial or antibiotic substances, or dyes (JP-A-63-209798, JP-A-1-268603, JP-A-3-10394), etc., may be mentioned.
Further, recently, a method of employing anthraquinones to inhibit sulfide production by sulfate-reducing bacteria, has been proposed (Japanese Patent 2,858,480, Japanese Patent 2,837,620, JP-A-2000-34202). It is considered that anthraquinones are reduced to anthrahydroquinones by microorganisms living under an anaerobic condition and penetrate into cell membranes of sulfate-reducing bacteria, whereupon they are oxidized to anthraquinones again and then inhibit the sulfate respiration metabolism, whereby formation of a sulfide is suppressed (Journal of Sewerage Monthly, No. 22, Vol. 6, p. 73).
Among the above methods, for example, use of nitrates or nitrites has an environmental problem, and iron sulfate has a possibility that depending upon the conditions, it itself becomes a supply source of sulfate ions. Further, these compounds are water-soluble and are likely to easily elute once substitution of water takes place due to e.g. rainfall at landfill sites. Accordingly, in order to maintain the effect for suppressing generation of hydrogen sulfide, it has been necessary to take a trouble of periodically additionally supplying such compounds. On the other hand, the method of employing anthraquinone compounds to suppress generation of hydrogen sulfide, is economical in that a long lasting effect can be obtained with a small amount, but commercially available anthraquinone compounds are usually in the form of a fine powder, and if such compounds are applied to landfill sites, the anthraquinone compounds will gradually flow out by e.g. rainfall, and periodical application has been required in order to maintain the effect.
Under these circumstances, it has been desired to develop a gypsum-based building material having an ability to suppress generation of hydrogen sulfide over a long period of time without periodical addition of a chemical agent, even when it is landfilled together with a large amount of organic substances.
Under these circumstances, the present invention has been made for the purpose of providing a gypsum-based building material which is capable of suppressing generation of hydrogen sulfide for a long period of time even when the gypsum-based building material is disposed or landfilled together with an organic substance.
The above object can be accomplished by a gypsum-based building material comprising gypsum as the main material and an anthraquinone compound incorporated.
Now, the present invention will be described in detail with reference to the preferred embodiments.
Under the above described circumstances, the present inventors have conducted an extensive study and as a result, have found that when an anthraquinone compound is incorporated in a certain amount to gypsum as the main material, such a gypsum-based building material has an ability to suppress generation of hydrogen sulfide over a long period of time even when all of the above-mentioned conditions for generation of hydrogen sulfide, are met. The anthraquinone compound has low solubility and is a compound which has no problem in safety by itself. With the gypsum-based building material prepared by incorporating an anthraquinone compound, the anthraquinone compound will be uniformly embedded among needle crystals when gypsum as the main material cures, and accordingly, when the gypsum is gradually dissolved in an anaerobic environment, a constant amount of the anthraquinone compound will also be always dissolved, whereby the effect will be remained over a long period of time as compared with a case where the anthraquinone compound was merely applied to a gypsum-based building material.
The anthraquinone compound to be used in the present invention is an anthraquinone represented by the structure (A) and may be any compound so long as it shows the effect of inhibiting sulfide production by sulfate-reducing bacteria. 
wherein each of R1 to R8 which are independent of one another, is a hydrogen atom, an alkyl group, an alkoxy group, a hydroxyl group, a halogen atom, a carboxyl group, a sulfo group or an amino group.
Here, the alkyl group may, for example, be an alkyl group such as a methyl group, an ethyl group, a n-propyl group, an i-propyl group, a n-butyl group, a t-butyl group, a n-pentyl group or a n-hexyl group, more preferably a C1-C6 alkyl group. The alkoxy group may, for example, be an alkoxy group such as a methoxy group, an ethoxy group, a n-propoxy group, a n-butoxy group, a t-butoxy group, a n-pentyloxy group or a n-hexyloxy group, more preferably a C1-C6 alkoxy group. Further, the halogen atom may, for example, be a fluorine atom, a chlorine atom or a bromine atom.
As a specific compound, anthraquinone (9,10-anthraquinone), 1-methylanthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone, 1-methoxyanthraquinone, 1-methoxy-4-methylanthraquinone, 1-hydroxyanthraquinone, 1,2-dihydroxyanthraquinone, 1,4-dihydroxyanthraquinone, 1,5-dihydroxyanthraquinone, 1,8-dihydroxyanthraquinone, 2,6-dihydroxyanthraquinone, 1-chloroanthraquinone, 2-chloroanthraquinone, 1,5-dichloroanthraquinone, 1,3-dibromoanthraquinone, anthraquinone-1-carboxylic acid, anthraquinone-2-carboxylic acid, 2-chloroanthraquinone-3-carboxylic acid, anthraquinone-2-sulfonic acid, 1-aminoanthraquinone, 2-aminoanthraquinone, 1,4-diaminoanthraquinone, or 1-amino-4-hydroxyanthraquinone, may, for example, be mentioned.
Further, the anthraquinone compound of the present invention includes anthrahydroquinones corresponding to the anthraquinones shown by the above structural formula (A). As a specific compound, anthrahydroquinone (9,10-anthracenediol), 1-methylanthrahydroquinone or 2-ethylanthrahydroquinone, may be mentioned. Further, such anthrahydroquinones include their alkali metal salts such as sodium salts. As a specific compound, a sodium salt (mono- or di-) of anthrahydroquinone may be mentioned.
Further, the anthraquinone compound of the present invention includes a dihydroanthraquinone compound, a tetrahydroanthraquinone compound and an octahydroanthraquinone compound corresponding to nucleus hydrogenated products of anthraquinones of the above structural formula (A). A specific compound may be 1,4-dihydroanthraquinone or 1,4,4a,9a-tetrahydroanthraquinone. Further, such nucleus hydrogenated products include tautomers and alkali metal salts. A specific compound may be a sodium salt (mono- or di-) of 1,4-dihydro-9,10-dihydroxyanthracene or 1,4-dihydro-9,10-hydroxyanthracene.
Among these anthraquinone compounds, anthraquinone is particularly preferred, since it is industrially readily available, and anthrahydroquinone as its reduction product, can easily be prepared by means of a reducing agent such as hydrosulfite. Of course, two or more of these anthraquinone compounds may be mixed for use.
The method of incorporating the anthraquinone compound of the present invention to the gypsum as the main material, is not particularly limited. It may be added to the gypsum in the form of a powder itself or in the state of an aqueous slurry, or it may be added in the form of an aqueous solution of the above-mentioned alkali metal salt or in the form of an organic solvent solution of an anthraquinone.
By such a method, the anthraquinone compound can be incorporated more uniformly. For example, gypsum is mixed with an aqueous solution of a disodium salt of anthraquinone or a disodium salt of 1,4-dihydro-9,10-hydroxyanthracene, followed by oxidation treatment or the like to precipitate anthraquinone, whereby the anthraquinone compound can be incorporated in the form of fine crystals.
The anthraquinone compound may be incorporated to gypsum not only in the above-mentioned form, but may preliminarily be mixed with an admixture as shown below and may be added to gypsum in a kneaded state or in a coated state. Further, it may preliminarily be incorporated to a raw material gypsum such as natural gypsum, desulfogypsum or phosphogypsum, which is independently commercialized and used for the production of cement or such a gypsum-based building material. Further, in the case of one having a surface material such as a lining paper for gypsum board on its surface, such as a gypsum board, the anthraquinone compound may be incorporated to the surface material.
The amount of the anthraquinone compound to be used in the present invention is usually from 0.005 to 5 parts by weight, preferably from 0.01 to 3 parts by weight, more preferably from 0.01 to 1 part by weight, per 100 parts by weight of gypsum. Such an anthraquinone compound has a higher effect for suppressing generation of hydrogen sulfide, as its amount increases. However, even if it is incorporated beyond 5 parts by weight, such tends to be costly disadvantageous, as compared with the above suppression effect. On the other hand, if the amount is less than 0.005 part by weight, no adequate effect for suppression can be obtained. The gypsum-based building material of the present invention thus obtained will exhibit the effect for suppressing generation of hydrogen sulfide over a long period of time against sulfate-reducing bacteria having an ability to reduce a sulfate, irrespective of the genus or species of the bacteria. For example, it is useful against those disclosed in xe2x80x9cJournal of Water and Wastexe2x80x9d No. 31, Vol. 4, p. 294-305 (1989). Typical bacteria include species belonging to genus Desulfovibrio such as Desulfovibrio desulfuricans, genus Desulfobacter such as Desulfobacter postgatei, and other genus such as genus Desulfobulbus, genus Desulfococcus, Desulfonema limicola, genus Desulfonema, genus Desulfosalcina, genus Desulfomonus, and genus Desulfotomacrum.
The gypsum-based building material of the present invention may be not only one formed into a plate shape using gypsum as the main material, such as a gypsum board, a gypsum sheathing board, a reinforced gypsum board, a gypsum lath board, a decorated gypsum board or a non-combustible laminated gypsum board, as defined in JIS A6901-1997, and a perforated gypsum board for acoustic use or a non-woven glass fiber-filled gypsum plate, as defined in JIS A6301, but also a powdery, paste or slurry building material using gypsum as the main material, such as a SL plaster, or a gypsum plaster or gypsum-based putty, as defined in JIS A6904-1997.
The above gypsum boards can be produced by a usual gypsum board production line. It is one obtained by adding a known admixture such as pulp fiber and/or glass fiber, a known defoaming agent, setting modifier, adhesion-increasing agent, etc. to xcex2-type hemihydrate gypsum, xcex1-type hemihydrate gypsum or a mixture thereof, as the main material, as the case requires.
Further, the gypsum plaster, the gypsum-based putty, etc., of the present invention can likewise be produced by usual production apparatus for gypsum plasters, gypsum-based putties, etc., and they are ones obtained by adding known light weight aggregates such as pearlite or vermiculite, and a known viscosity-adjusting agent, setting modifier or the like to xcex2-type hemihydrate gypsum, xcex1-type hemihydrate gypsum or a mixture thereof, as the case requires.
With respect to any one of building materials, the anthraquinone compound can be incorporated by the above method of addition in the respective process for its production, and the anthraquinone compound can be uniformly embedded in the gypsum, while the gypsum as the main material and the anthraquinone compound will not present any adverse effect to the gypsum itself during the production, or without creating any problem in the production line of the gypsum-based building material. Further, the term xe2x80x9cadditionxe2x80x9d used in this specification is meant for one form of incorporation.